Preheat the oven to 350°F. Grease three 6-inch cake pans and line the bottoms with parchment paper rounds. Set aside.

In a large bowl, whisk together the sugar, buttermilk, canola oil, eggs, and vanilla extract until smooth. Then, add the flour, baking soda, salt, and cocoa powder. Whisk just until the batter forms – don't over-mix!

Divide the batter evenly between the 3 cake pans (if you're using a scale, each should have about 315g of batter). Smooth with an offset spatula. Place the cake pans on a sheet pan.

Bake the cakes for 22-23 minutes, until an inserted toothpick has just a few moist crumbs on it. Let the cakes cool in the pans for about 5 minutes. Then, use a knife to loosen the cakes from the sides of the pans. Carefully flip the cakes out of the pans and let them cool completely on a wire rack.

In a large bowl, beat the butter and chocolate-hazelnut spread until it's light and fluffy, 2-3 minutes. Add the cocoa powder and mix until smooth.

Next, mix in the powdered sugar 1 cup at a time until a thick frosting forms. Add a pinch of salt and 3 Tablespoons of milk. Continue adding milk, 1 Tablespoon at a time, until you reach your desired texture. (The buttercream should be thick but spreadable.)

Whip the buttercream for 2-3 minutes until it's fluffy. Set aside.

Using a serrated bread knife, cut the domes off of the tops of the cakes.

Place one cake round on a plate or cake stand. Spread a thick layer of frosting on top. Top with another cake round, add frosting to the second layer, and top with the third cake round until you have a three layer cake.

Frost the outside of the cake and use a bench scraper to smooth out the sides. Decorate as desired. Slice and enjoy with hot coffee or milk!